Polarization-preserving optical fibers have been sought for some time because maintaining linear polarization is important for efficient coupling between single-mode fibers and polarization sensitive optical devices and for achieving maximum gains in fiber Raman and parametric oscillators and amplifiers.
It has been known in the prior art that polarization may be preserved by a fiber that has a noncircular shape and/or is birefringent. One prior art method has induced an elliptically shaped core in a fiber by collapsing a preform with a slight vacuum in the center. Another approach is illustrated by U.S. Pat. No. 3,535,017, issued to S. E. Miller on Oct. 20, 1970, in which a transmitting fiber is deformed into an asymmetric shape.
The problem addressed by the present invention is that of producing a polarization-preserving fiber resistant to the polarization-mixing effects of handling, simple to fabricate and of consistent quality.